Ceramic capacitors comprise at least two electrical conductors between which a dielectric (insulating) ceramic layer is arranged. The properties of ceramic capacitors are essentially determined by the polarization properties of the ceramic dielectric. Materials which have a spontaneous polarization in the absence of an electric field are referred to as pyroelectric. If the direction of the spontaneous polarization can be changed by an electric field (or a mechanical stress) being applied, the materials are called ferroelectric. If, during the phase transition from the paraelectric phase, the ions of a ferroelectric are not displaced parallel to one another, but rather antiparallel to one another, the material is referred to as antiferroelectric.
One ceramic material that has been used heretofore principally for piezoelements is the lead zirconate titanate system (Pb(ZrxTi1−x)O3 or PZT). The latter constitutes a solid solution (continuous solid solution series) of the antiferroelectric lead zirconate (PbZrO3) and the ferroelectric lead titanate (PbTiO3, PTO), which can have both ferroelectric and antiferroelectric properties depending on the composition. The phase diagram in FIG. 1 shows how the Curie temperature and crystal symmetry of the PZT system depend on the composition thereof. FT and FR are ferroelectric tetragonal and rhombohedral phases, respectively. PC denotes the paraelectric cubic phase. AO and AT stand for antiferroelectric orthorhombic and tetragonal phases, respectively. HT stands for the high-temperature phase, and LT stands for the low-temperature phase. Proceeding from PTO, the Curie point is reduced from 490° C. (Tc (PTO)) to 230° C. (Tc (PZO)) in the case of substitution of titanium ions by zirconium ions; in this case, the symmetry changes from FT through FR to AO (at room temperature). PZT is paraelectric above Tc. When the temperature falls below the Curie temperature, virtually a distortion of the cubic structure takes place, to be precise depending on the Zr/Ti ratio. In other words, the Ti-rich PZT solid solutions are ferroelectric and tetragonal at room temperature, in contrast to the Zr-rich PZT solid solutions, which are antiferroelectric-orthombic (O-phase) or ferroelectric-rhombohedral. PZT materials have been used heretofore principally for piezoelements, e.g. piezoactuators. The piezoelectric properties required therefor are particularly pronounced at the so-called morphotropic phase boundary (MPB), which separates the two FE phases (FT and FR); in this case, two different crystal structures form only after slight variation of the ZrTi ratio. The MPB lies between PbZr0.6Ti0.4O3 and PbZr0.55Ti0.45O3.
WO 2011/085932 A1 discloses a capacitor comprising a heating element and a capacitor region comprising dielectric layers and internal electrodes arranged between the dielectric layers, wherein the heating element and the capacitor region are thermally conductively connected to one another.
It could therefore be helpful to provide a ceramic material suitable for capacitors using multilayer technology and having improved properties.